The objectives of this proposal are to define reproducible conditions that permit: (1) enzymatic dispersion of rat lung into single, viable cells, (2) the separation of this heterogeneous mixture of single cells (by centrifugation on a Ficoll gradient) into populations containing type II alveolar pneumonocytes, (3) subsequent culture of the type II alveolar cells. Lungs obtained from 40-60 gram rats will be enzymatically dispersed into single cells. This suspension of single cells will be separated into homogeneous populations on a sterile gradient of Ficoll in tissue culture medium. Type II cells, thus isolated will be grown in vitro as monolayer cultures. At all steps (enzymatic dispersion, density gradient separation, culture) the preparation will be monitored by electron microscopy to identify the presence of type II alveolar pneumonocytes on the basis of morphological (osmiophilic lamellar bodies) and cytochemical (peroxisomes) markers.